Static electronic lens for electron beam valves



Dec. 29, 1959' B. HENSEL STATIC ELECTRONIC LENS FOR ELECTRON BEAM VALVESFiled Feb. 16, 1954 United States Patent STATIC ELECTRONIC LENS FORELECTRON BEAM VALVES Bernhard Hensel, Berlin-Friedenau, Germany,assignor to Loewe Opta Aktiengesellschaft, Berlin-Steglitz, Germany, acompany of Germany The familiar static electronic lenses for electronbeam valves are usually shaped as follows:

Seen in the direction of the beam, the first anode behind the Wehneltcylinder is followed by a tubular second anode; behind the latter isarranged, at a definite distance of one or several centimeters, anothercoaxial tube which is fed, as is the first one, with the high anodevoltage (A -voltage). In the gap between these two anode tubes a thirdtube is arranged, the length of which corresponds approximately to thedistance between the two anode tubes, and the diameter of which isseveral millimeters larger than that of the anode tubes. Thisintermediate tube .is either fed with a positive voltage which is incomparison much lower than the anode voltage or joined directly to thecathode. The intermediate electrode can be either just as long as thedistance between the two anode tubes or a little longer or shorter.

In any case, in the familiar manner electric potential fields form atthe transition points between the two anodes and the intermediate tube,andvconcentrate the electronic beam running through the tube axis.

If d is the diameter of the anode tubes and D the somewhat largerdiameter of the intermediate tube, the desired electrostatic lens effectwill be most perfectly achieved when the quotient d:D has a definitevalue. In the usual electrode systems this value amounts to about 0.7 to0.9. For these reasons, the diameter d of the anode tubes is usuallyfixed at from to millimetersand the di-. ameter D of the intermediateelectrode at from 12 to millimeters.

Now the inventor has noted, particularly when working at constructionaldevelopment, that it is of advantage to combine the whole staticelectrode system described above in such a manner that instead of thesingle tubular electrodes being mounted, as hitherto, on glass or otherinsulating rods arranged parallel -to the tube axis, the whole system isdesigned as one integral member. a design will be accomplished thebetter the lighter .the individual static electrodes are, which weredescribed above and which form the lens system. Contrary to thiscondition is the other condition, mentioned above, that the diameter dof the external anode tubes must not be smaller than a fixed value.

The present invention advantageously surmounts the difficulties whichthus arise. Incontestable experiments have shown that to maintain therequired ratio of d to D, it is only necessary to provide this diameterd at those points of the anode tubes which are directly at the origin ofthe lens fields, i.e. at the transition to the edges of the intermediateelectrode. The diameter of the rest of the anode tubes, however, isunimportant for the production of the lens effect. On the basis of thisknowledge and in accordance with the present invention, the anode tubesof an, in particular, tripartite static system of electronic lenses areprovided with a much smaller diameter than hitherto, in particular witha diameter that can be substantially smaller than the diameter D of thetubular intermediate electrode. Only at those edges of the anode tubesfacing the inside, in other words, at the point where the lens potentialfields arise, the diameter d is so 'fixed that the desired value d:D=O.7to 0.9 is still achieved. Accordingly, the anode tubes are provided witha funnel-shaped enlargement at the ends near the intermediate tube andhave for the rest of their length only a relatively small diameter of afew millimeters. Thus a considerable saving in weight is achieved andthe electronic lens can be designed so small and light that the singleelectrodes need not be fastened to individual mounting rods but can becombined without any constructional difficulties into one integralwhole. The drawing shows one example of this invention, in a simplifiedarrangement of the three electrodes belonging to a static lens system ofthe common manner of operation: The tubular intermediate electrode .1which is kept on a low voltage has a diameter D of a normal size of from15 to 20 millimeters. edges of the two tubes 2 and 3, which are kept ona high 2 potential whereby, at the transition points 4 and 5 and in Suchthe familiar manner, the static fields which give rise to the lenselfect are formed. According to the invention, the tubes 2 and 3, whichmust, at the transition points 4 and 5, have a definite diameter d thatmust not be much smaller than the diameter D, are enlarged at 6 or 7 ina funnel shaped fashion, so that the exterior edge of the funnel attainsthe required diameter d. The rest of the anode tubes 2 and/or 3,however, has a much smaller diameter of e.g. only a few millimeters.This small diameterneed only be large enough to allow the beam, whichhas not yet been deflected at this point, to pass without touching thewalls of the tubes 2 and 3.

Furthermore, it is often customary to provide the edges of the anodetubes at the transition points 4 and 5 with a calotte-shaped covercurved towards the interior of the tube and provided, as a perforateddiaphragm, with a central aperture. This method, too, can in principlebe realized, in connection with the presentinvention, by providing, e.g.at that spot of each anode tube at which the conical enlargement 6 or 7begins, a perforated diaphragm 8 or 9. The cathode 11 and an electrodeWehnelt 12 are mounted in .the usual manner on a glass base 10. Thefirst anode 13 .is arranged betweensaid electrode Wehnelt and thecylindrical electrode 3. A low tension voltage source L.T. is providedbetween said cathode 11 and said first anode 1-3, and-a high tensionvoltage source HT. is connected with its negative pole to the positivepole of the LT. voltage source and with its positive pole to 'said hightension electrodes 2 and 3.

What I claim is:

, 1. An electrostatic lens arrangement comprising, in combination, apair of tubular, axially aligned, inner electrodes, each of saidelectrodes having a body portion and an outwardly flaring end portion,said end portions being located opposite and spaced from each other; andan outer, tubular lens electrode arranged coaxially with said innerelectrodes and enclosing the space between said outwardly flaring endportions and at least said outwardly flaring end portions themselves,whereby the opposite ends of said outer lens electrode are relativelywidely spaced from the respective body portions of said innerelectrodes, and the danger of corona discharge from said opposite endsto the respective inner electrodes when said outer lens electrode ismaintained at a potential which is substantially more negative than thatof said inner electrodes is substantially lessened.

2. An electrostatic lens arrangement comprising, in combination, a pairof tubular, axially aligned, inner electrodes, each of said electrodeshaving a body portion and an outlwardly flaring end portion, said endportions being Opposite its external edges are the located opposite andspaced from each other, and an outer, tubular lens electrode arrangedcoaxially with said inner electrodes and in the space between saidoutwardly flaring end portions, whereby the opposite ends of said outerlens electrode are relatively widely spaced from the respective bodyportions of said inner electrodes, the danger of corona discharge fromsaid opposite ends to the respective inner electrodes beingsubstantially lessened when said outer lens electrode is maintained at apotential which is substantially more negative than that of said innerelectrodes.

3. An electrostatic lens arrangement comprising, in combination, a pairof tubular, axially aligned, inner electrodes, each of said electrodeshaving a body portion and an outwardly flaring end portion, said endportions being located opposite and spaced from each other, and anouter, tubular lens electrode arranged coaxially with said innerelectrodes and located Within the space between and adjacent saidoutwardly flaring end portions of said inner electrodes, the oppositeends of said outer lens electrode being relatively widely spaced fromthe respective body portions of said inner electrodes, whereby thedanger of corona discharge from the opposite ends of said outer lenselectrode to the respective inner electrodes is substantially lessenedwhen said outer lens electrode is maintained at a potential which issubstantially more negative than that of said inner electrodes.

4. An electrostatic lens arrangement comprising, in

combination, a pair of tubular, axially aligned, inner electrodes, eachof said electrodes having a body portion and an outwardly flaring endportion, said outwardly flaring end portions being located opposite andspaced from each other, an an outer, tubular lens electrode terminatingin opposite edges and arranged coaxially with said inner electrodes andwithin the space between said outwardly flaring end portions, wherebythe opposite edges of said outer lens electrode are relatively widelyspaced from the respective body portions of said inner electrodes, thedanger of corona discharge from said opposite edges to the respectiveinner electrodes being substantially lessened when said outer lenselectrode is maintained at a potential which is substantially morenegative than that of said inner electrodes.

5. An electrostatic lens arrangement comprising, in

at least one of said flaring end portions being conically shaped, and anouter, tubular lens electrode arranged coaxially with said innerelectrodes and having a diameter greater than said outwardly flaring endportions of said inner electrodes, said outer lens electrode terminatingin opposite ends and being located in the space between said outwardlyflaring end portions of said inner electrodes, the opposite ends of saidouter lens electrode 4 I a being relatively widely spaced fromtherespective body portions of said inner electrodes, the danger ofcorona discharge from said opposite ends to the respective innerelectrodes being substantially lessened when said outer lens electrodeis maintained at a potential which is substantially more negative thanthat of said inner electrodes.

6. An electrostatic lens arrangement comprising, in combination, atleast one tubular inner electrode having a body portion and an outwardlyflaring end portion, and an outer, tubular lens electrode arrangedcoaxially with said inner electrode and located within the space betweensaid outwardly flaring end portion and at leastthe outwardly flaring endportion itself, whereby the end of said outer lens electrode which isclosest to said inner electrode is relatively widely spaced from thebody portion of said inner electrode, and danger of corona dischargefrom said end of said outer lens electrode to said inner electrode, whensaid outer lens electrode is maintained at a potential which issubstantially more negative than said inner electrode, is substantiallylessened.

7. An electrostatic lens arrangement comprising, in

combination, a hollow cylindrical inner electrode having 1,

a body portion and a conically shaped outwardly flaring end portion, anan outer, tubular lens electrode arranged coaxially with said innerelectrode and enclosing the space between said outwardly flaring endportion and at least the outwardly flaring end portion itself, wherebythe end of said outer lens electrode which is closest to said innerelectrode is relatively widely spaced from the body portion of saidinner electrode, and danger of corona discharge from said end of saidouter lens electrode to said inner electrode, when said outer lenselectrode is maintained at a potential which is substantially morenegative than said inner electrode, is substantially lessened.

I 8. An electrostatic lens arrangement comprising, in combination, ahollow cylindrical inner electrode having abody poition'and aflange-shaped outwardly flaring end portion, and an outer, tubular lenselectrode arranged coaxially with said inner electrode and enclosing thespace between said outwardly flaring end portion and at least theoutwardly flaring end portion itself, whereby the end of said outer lenselectrode which is closest to said inner electrode is relatively widelyspaced from the body portion of said inner electrode, and danger ofcorona discharge from said end of said outer lens electrode to saidinner electrode, when said outer lens electrode is maintained at apotential which is substantially more negative than said innerelectrode, is substantially lessened.

References Cited in the file of this patent UNITED STATES PATENTS2,219,405 Sukumlyn Oct. 29, 1940 2,226,107 Schlesinger Dec. 24, 19402,405,611 Samuel Aug. 13, 1946 2,476,060 Moss July 12, 1949

